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Five Sneak Previews From "Before and After"

Below are five sneak peeks from Thursday night's all-new episode of Grey's Anatomy, "Before and After." The big Grey's Anatomy-Private Practice crossover is in full effect, with Addison & Co. at Seattle Grace with her ailing brother, Archer (Grant Show).

Follow the jump for four more previews, in which Derek reunites with old friend Sam (Taye Diggs), Izzie gives the interns their daily assignment, Lexie pressuring Mark to go public with their relationship, and Sam and Mark poking fun at Bailey's new career path ...

MEREDITH: "You don't get to call me a whore. When I met you, I thought I had found the person that I was going to spend the rest of my life with. I was done! All the boys and all the bars and all the obvious daddy issues, who cares? I was done. You left me. You chose Addison. I'm all glued back together now. I make no apologies for how I chose to repair what you broke. You don't get to call me a whore."DEREK: "This thing with us is finished. It's over."MEREDITH: "Finally."DEREK: "Yeah, it's done."MEREDITH: "It is done."